Re: [PATCHv2 2/2] xtensa: use buddy allocator for PTE table

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Max Filippov wrote:
> On Mon, Oct 14, 2013 at 6:32 PM, Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
> > At the moment xtensa uses slab allocator for PTE table. It doesn't work
> > with enabled split page table lock: slab uses page->slab_cache and
> > page->first_page for its pages. These fields share stroage with
> > page->ptl.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Cc: Chris Zankel <chris@zankel.net>
> > Cc: Max Filippov <jcmvbkbc@gmail.com>
> > ---
> > v2:
> >  - add missed return in pte_alloc_one_kernel;
> >
> >  arch/xtensa/include/asm/pgalloc.h | 20 ++++++++++++--------
> >  arch/xtensa/include/asm/pgtable.h |  3 +--
> >  arch/xtensa/mm/mmu.c              | 20 --------------------
> >  3 files changed, 13 insertions(+), 30 deletions(-)
> >
> > diff --git a/arch/xtensa/include/asm/pgalloc.h b/arch/xtensa/include/asm/pgalloc.h
> > index b8774f1e21..8507b32d6e 100644
> > --- a/arch/xtensa/include/asm/pgalloc.h
> > +++ b/arch/xtensa/include/asm/pgalloc.h
> > @@ -38,14 +38,18 @@ static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
> >         free_page((unsigned long)pgd);
> >  }
> >
> > -/* Use a slab cache for the pte pages (see also sparc64 implementation) */
> > -
> > -extern struct kmem_cache *pgtable_cache;
> > -
> >  static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm,
> >                                          unsigned long address)
> >  {
> > -       return kmem_cache_alloc(pgtable_cache, GFP_KERNEL|__GFP_REPEAT);
> > +       pte_t *ptep;
> > +       int i;
> > +
> > +       ptep = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT);
> > +       if (!ptep)
> > +               return NULL;
> > +       for (i = 0; i < 1024; i++, ptep++)
> > +               pte_clear(NULL, 0, ptep);
> > +       return ptep;
> 
> You're returning modified ptep, not the allocated one.

Erghh.. Stupid me.

Corrected patch below.

From 0ba2ac687321f5ad7bac5f5c141da5b65b957fdc Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Mon, 14 Oct 2013 13:38:21 +0300
Subject: [PATCHv3] xtensa: use buddy allocator for PTE table

At the moment xtensa uses slab allocator for PTE table. It doesn't work
with enabled split page table lock: slab uses page->slab_cache and
page->first_page for its pages. These fields share stroage with
page->ptl.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
---
v3:
 - return correct value from pte_alloc_one_kernel();
v2:
 - add missed return in pte_alloc_one_kernel();

 arch/xtensa/include/asm/pgalloc.h | 20 ++++++++++++--------
 arch/xtensa/include/asm/pgtable.h |  3 +--
 arch/xtensa/mm/mmu.c              | 20 --------------------
 3 files changed, 13 insertions(+), 30 deletions(-)

diff --git a/arch/xtensa/include/asm/pgalloc.h b/arch/xtensa/include/asm/pgalloc.h
index b8774f1e21..d38eb9237e 100644
--- a/arch/xtensa/include/asm/pgalloc.h
+++ b/arch/xtensa/include/asm/pgalloc.h
@@ -38,14 +38,18 @@ static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 	free_page((unsigned long)pgd);
 }
 
-/* Use a slab cache for the pte pages (see also sparc64 implementation) */
-
-extern struct kmem_cache *pgtable_cache;
-
 static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm,
 					 unsigned long address)
 {
-	return kmem_cache_alloc(pgtable_cache, GFP_KERNEL|__GFP_REPEAT);
+	pte_t *ptep;
+	int i;
+
+	ptep = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT);
+	if (!ptep)
+		return NULL;
+	for (i = 0; i < 1024; i++)
+		pte_clear(NULL, 0, ptep + i);
+	return ptep;
 }
 
 static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
@@ -59,7 +63,7 @@ static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
 		return NULL;
 	page = virt_to_page(pte);
 	if (!pgtable_page_ctor(page)) {
-		kmem_cache_free(pgtable_cache, pte);
+		__free_page(page);
 		return NULL;
 	}
 	return page;
@@ -67,13 +71,13 @@ static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
 
 static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
 {
-	kmem_cache_free(pgtable_cache, pte);
+	free_page((unsigned long)pte);
 }
 
 static inline void pte_free(struct mm_struct *mm, pgtable_t pte)
 {
 	pgtable_page_dtor(pte);
-	kmem_cache_free(pgtable_cache, page_address(pte));
+	__free_page(pte);
 }
 #define pmd_pgtable(pmd) pmd_page(pmd)
 
diff --git a/arch/xtensa/include/asm/pgtable.h b/arch/xtensa/include/asm/pgtable.h
index 0fdf5d043f..216446295a 100644
--- a/arch/xtensa/include/asm/pgtable.h
+++ b/arch/xtensa/include/asm/pgtable.h
@@ -220,12 +220,11 @@ extern unsigned long empty_zero_page[1024];
 #ifdef CONFIG_MMU
 extern pgd_t swapper_pg_dir[PAGE_SIZE/sizeof(pgd_t)];
 extern void paging_init(void);
-extern void pgtable_cache_init(void);
 #else
 # define swapper_pg_dir NULL
 static inline void paging_init(void) { }
-static inline void pgtable_cache_init(void) { }
 #endif
+static inline void pgtable_cache_init(void) { }
 
 /*
  * The pmd contains the kernel virtual address of the pte page.
diff --git a/arch/xtensa/mm/mmu.c b/arch/xtensa/mm/mmu.c
index a1077570e3..c43771c974 100644
--- a/arch/xtensa/mm/mmu.c
+++ b/arch/xtensa/mm/mmu.c
@@ -50,23 +50,3 @@ void __init init_mmu(void)
 	 */
 	set_ptevaddr_register(PGTABLE_START);
 }
-
-struct kmem_cache *pgtable_cache __read_mostly;
-
-static void pgd_ctor(void *addr)
-{
-	pte_t *ptep = (pte_t *)addr;
-	int i;
-
-	for (i = 0; i < 1024; i++, ptep++)
-		pte_clear(NULL, 0, ptep);
-
-}
-
-void __init pgtable_cache_init(void)
-{
-	pgtable_cache = kmem_cache_create("pgd",
-			PAGE_SIZE, PAGE_SIZE,
-			SLAB_HWCACHE_ALIGN,
-			pgd_ctor);
-}
-- 
 Kirill A. Shutemov

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